The present invention relates to a rotary pump with an immersed rotor, in particular for use in taking up and then delivering liquids, such as hydrocarbons, that come from chemical processes.
Immersed-rotor rotary pumps known in the prior art generally comprise a pump wheel rotated by an electric motor. The electric motor is constituted by a stator element or xe2x80x9cstatorxe2x80x9d, mounted in a case, and a rotor element or xe2x80x9crotorxe2x80x9d that directly engages the pump wheel. A fraction of the liquid taken up by the pump is diverted to act as a cooling liquid in which the rotor is immersed. The stator of the motor is protected from said cooling liquid by a leakproof wall.
The cooling liquid flowing over the outer wall of the rotor constitutes a mass which does indeed oppose rotation of the rotor, but which above all gives rise to a considerable increase in the radial inertia of the rotor, whatever its speed, because of the small size of the magnetic gap of the motor (about 1 mm). This additional inertia is proportional to R/xcex5 (where R is the radius of the rotor and xcex5 is the gap) and it is very harmful to obtaining stable and robust control of means for supporting and guiding the rotor, such as magnetic bearings.
The present invention seeks to remedy the above-mentioned drawbacks, and in particular to improve the stability and the quality of the control applied to the means for supporting and guiding the rotor of an immersed-rotor rotary pump.
To this end, the present invention proposes adding liquid recirculation grooves so as to increase the overall magnetic gap virtually, thereby reducing the above-mentioned phenomenon of radial inertia of the rotor.
For example, if the magnetic gap is 200 mm long and 1 mm across, four grooves that are 10 mm long (giving a total of 40 mm) and 10 mm deep can reduce the above-mentioned phenomenon by a ratio of one to two:   (                    40        200            xc3x97              10        1              =    2    )
More particularly, the invention provides a rotary pump for taking in liquid, the pump comprising a pump wheel secured to a rotor immersed in a portion of said liquid taken in by the pump, a motor comprising a stator element mounted in a case and a rotor element mounted on the rotor to rotate the rotor about an axis, means for supporting and guiding the rotor, and protection means for protecting the stator element of the motor from said liquid, the pump being characterized in that the rotor comprises at least one groove in an outer surface covered by said portion of the liquid, in particular to reduce inertial effects during radial displacements and due to said portion of the liquid.
In order to facilitate the flow of the liquid over the outer surface of the rotor, the groove can be formed over the entire outline of the rotor. The outline can be situated, for example, in a plane that is substantially perpendicular to the axis of rotation.
The support and guidance means most commonly used in rotary pumps of the prior art comprise smooth mechanical bearings which are lubricated by the liquid taken in by the pump. Such bearings can frequently be stressed in abnormal manner, in particular in the event of the liquid evaporating or in the event of cavitation in the pump. They must therefore be changed periodically, thereby giving rise to a high level of cost and requiring the user to open up the pump.
In the present invention, the rotor is supported and guided by magnetic bearings which do not require any special maintenance.
In a first embodiment of the invention, the support and guide means comprise at least one radial active magnetic bearing of the cylindrical type for servo-controlling the radial position of the rotor on a radial equilibrium position, and axial active magnetic bearings for servo-controlling the axial position of the rotor on an axial equilibrium position. The radial active magnetic bearing is preferably a self-detecting bearing, i.e. a bearing suitable on its own for detecting the radial position of the rotor. For servo-control of the axial position of the rotor, an axial position detector is nevertheless provided at one end of the rotor. The axial active magnetic bearings then servo-control the axial position of the rotor as a function of position information provided by the detector.
In a second embodiment of the invention, the support and guidance means comprise active magnetic bearings of the conical type for servo-controlling both the radial and the axial positions of the rotor on respective equilibrium positions. Each of the conical active magnetic bearings is suitable for detecting the radial position of the rotor. The axial position of the rotor is detected by an axial position detector mounted at one end of the rotor.
In both of the above embodiments, the use of self-detecting magnetic bearings makes it possible to reduce the cost of manufacturing the pump compared with using distinct radial position detectors for the radial bearings.
The above-specified cylindrical or conical radial magnetic bearings can be homopolar or heteropolar.
Typically, the protection means is constituted by a jacket preventing said portion of the liquid that covers the rotor from penetrating into a cavity of the case in which the stator element of the motor is mounted. Said cavity of the case can be filled with a substance that has been injected under pressure (elastomer, epoxy resin, sand) to reinforce the protection of the stator element of the motor against the portion of the liquid that covers the rotor.
A bore can be formed in the rotor along its axis of rotation to convey said portion of the liquid that covers the rotor towards the pump wheel from the end of the rotor that is remote from the pump wheel. The bore makes it possible to minimize liquid circulation over the outer surface of the rotor, thereby limiting the axial loading applied to the bearings and to the motor.
Given that the pump is usually to be found in a dangerous area, means must be provided to prevent any explosion at the electrical connections. In the invention, an explosion-proof and leakproof compartment is included in the case to house the electronic power supply and control circuits for the guide means, i.e. the magnetic bearings. A first explosion-proof junction box fixed to the case enables said electronic circuits to be electrically connected to the electricity mains. A second explosion-proof junction box fixed to the case enables the motor to be connected to the electricity mains.
Advantageously, the means for supporting and guiding the rotor comprise first and second radial active magnetic bearings disposed at opposite ends of the motor and liquid recirculation grooves are provided in the outer surface of the rotor in zones situated between the motor and each of the first and second radial magnetic bearings so as to reduce the inertial effects due to said portion of the liquid.